Patients with recurrent malignant glioma treated with bevacizumab, a monoclonal antibody to vascular endothelial growth factor (VEGF), alone or in combination with irinotecan have had impressive reductions in MRI contrast enhancement and vasogenic edema. Responses to this regimen, as defined by a decrease in contrast enhancement, have led to significant improvements in progression-free survival rates but not in overall survival duration. Some patients for whom this treatment regimen fails have an uncharacteristic pattern of tumor progression, which can be observed radiographically as an increase in hyperintensity on T2-weighted or fluid-attenuated inverse recovery (FLAIR) MRI. To date, there have been no reports of paired correlations between radiographic results and histopathologic findings describing the features of this aggressive tumor phenotype. In this study, we correlate such findings for 3 illustrative cases of gliomas that demonstrated an apparent phenotypic shift to a predominantly infiltrative pattern of tumor progression after treatment with bevacizumab. Pathologic examination of abnormal FLAIR areas on MRI revealed infiltrative tumor with areas of thin-walled blood vessels, suggesting vascular “normalization,” which was uncharacteristically adjacent to regions of necrosis. High levels of insulin-like growth factor binding protein-2 and matrix metalloprotease-2 expression were seen within the infiltrating tumor. In an attempt to better understand this infiltrative phenotype associated with anti-VEGF therapy, we forced a highly angiogenic, noninvasive orthotopic U87 xenograft tumor to become infiltrative by treating the mice with bevacizumab. This model mimicked many of the histopathologic findings from the human cases and will augment the discovery of alternative or additive therapies to prevent this type of tumor recurrence in clinical practice.

Initiation and maintenance of several cancers including glioblastoma (GBM) may be driven by a small subset of cells called cancer stem cells (CSCs). CSCs may provide a repository of cells in tumor cell populations that are refractory to chemotherapeutic agents developed for the treatment of tumors. STAT3 is a key transcription factor associated with regulation of multiple stem cell types. Recently, a novel autocrine loop (IL-6/STAT3/HIF1alpha) has been observed in multiple tumor types (pancreatic, prostate, lung, and colon). The objective of this study was to probe perturbations of this loop in a glioblastoma cancer stem cell line (GSC11) derived from a human tumor by use of a JAK2/STAT3 phosphorylation inhibitor (WP1193), IL-6 stimulation, and hypoxia. A quantitative phosphoproteomic approach that employed phosphoprotein enrichment, chemical tagging with isobaric tags, phosphopeptide enrichment, and tandem mass spectrometry in a high-resolution instrument was applied. A total of 3414 proteins were identified in this study. A rapid Western blotting technique (<1 h) was used to confirm alterations in key protein expression and phosphorylation levels observed in the mass spectrometric experiments. About 10% of the phosphoproteins were linked to the IL-6 pathway, and the majority of remaining proteins could be assigned to other interlinked networks. By multiple comparisons between the sample conditions, we observed expected changes and gained novel insights into the contribution of each factor to the IL6/STAT3/HIF1alpha autocrine loop and the CSC response to perturbations by hypoxia, inhibition of STAT3 phosphorylation, and IL-6 stimulation.

Glioblastoma multiforme (GBM) is the most common and malignant form of primary brain tumors. It is highly invasive and current treatment options have not improved the survival rate over the past twenty years. Novel approaches and technologies from systems biology have the potential to identify biomarkers that could serve as new therapeutic targets for GBM. This study employed